Frontal pole impacts present a problem for passenger compartment electronic sensing devices used for determining if an air bag should be deployed or not, and if so, at what time. This is due to the relatively soft initial impact that poles apply to the vehicle which results in a velocity vs. time profile which is similar to that of a 9 MPH frontal barrier impact. In the case of the pole impact, deployment of the air bag is desirable whereas a 9 MPH frontal barrier impact should not cause the air bag to be deployed.
FIG. 1 graphically illustrates the problem. The 30 MPH center high pole impact for the vehicle involved, does not distinguish itself from the 9 MPH frontal barrier impact until 58 msec into the crash which is 15 msec after the optimal time for firing the driver side air bag.
Initially, it will be noted that the velocity curve of the 30 MPH pole is far more "wavy" than the 9 MPH barrier during the early portion of the crash. This means that the acceleration trace of the pole impact had far more oscillation than the 9 MPH barrier. FIG. 2 shows the deceleration of the vehicle during a 30 MPH center high pole crash. The peak in deceleration at 5 msec corresponds to the bumper collapse, and the peak at 25 msec into the crash corresponds to the radiator/tie bar collapse. The final, major deceleration starting at 40 msec corresponds to the pole contacting the engine. The engine quickly contacts the front of the dash and the car stops abruptly. Between the major structural components very little resistance is felt by the pole during the crash, and the pole quickly passes through the car . This lack of resistance during the pole crash is what makes electronic based sensing of the crash difficult. Comparing the velocity traces in FIG. 1 the 30 MPH pole is actually less severe than the 9 MPH frontal barrier during the initial 60 msec of the crash.
FIG. 3 shows that the deceleration of the passenger compartment is closely proportional to the frontal barrier forces. By comparing FIGS. 2 and 3 one can conclude that during the pole impact the vehicle experience pulse type forces (large values for short time periods) while the 9 MPH frontal barrier the vehicle experienced relatively constant type forces. The pulse type forces felt by the passenger compartment during the pole crash are believed to be the cause of the observed higher acceleration oscillation relative to the 9 MPH frontal barrier crash.